In gens 5-7, I thought the reason Game Freak stopped making cross-gen evos was because it would break Eviolite continuity - for example a Ledian holding an Eviolite would not get a stat boost in gen 5 because it cannot evolve, so Ledian wouldn't be able to get a cross-gen evo, otherwise continuity would be broken. Mega Evolutions were a way to be able to buff old Pokemon without breaking this continuity. Branching evos are fine, like Eevee getting Sylveon in gen 6, since that's consistent with Eviolite on Eevee. Friendship evos could be explained with... I guess everyone fucking hates Golbats in Kanto. (you're actually prevented from evolving Golbat into Crobat in FRLG until you unlock the national dex I believe, which I always found fascinating)

Continuity was also why they always had to have a mossy rock/icy rock to evolve Leafeon and Glaceon. Leaf Stone has been a thing since gen 1, but it wasn't until recently you were allowed to use it for Leafeon.
They seemed to stop caring about evolution continuity around gen 8, with Obstagoon etc. We've seen a good amount of cross-gen evolutions since.
They've even changed the evolution method for some mons, like Milotic - though all of the new evolution methods are usually explained with "the item doesn't exist in this region". What isn't explainable is the Leafeon/Glaceon retcon, you can now evolve them with stones, despite those stones existing in the games where you have to use the icy/mossy rock method.

Continuity has been broken with BST and type changes even before all this as well, so do you think the pause in gens 5-7 for cross-gen evolutions was more of them prioritizing other things than keeping Eviolite consistent? How do you feel about Pokemon continuity not being set in stone, especially for flat-out retcons ie Leafeon/Glaceon?

Personally I don't really care about continuity. I just thought that was why they stopped doing cross-gen evos. I'm glad they're back, every single one has been amazing.